If you're a registered user, you might have noticed there is a little green icon next to all the titles of shows, episodes, people, networks, etc. That's the edit/contribute button. Anyone can use it to add or edit information on any existing show, person or network page.
The only limitation as a new user is the ability to add new pages(shows, person, network). For that you currently need to be made a trusted contributor.(More info on user permissions)